In relation to remote control devices, it is commonly known to take steps to ensure that any given remote controlled unit may only be operated by a particular remote control unit and that, on the other hand, the activation of any such given remote control unit will not result in activation of (an)other remote-controlled unit or units than those intended.
Thus, it is known to provide a remote control with a code which is transmitted together with a command signal to the unit to be operated. The unit will know the code and upon receipt of the command signal, it will test whether the right code is transmitted and, if this is the case, carry out the desired command. This technique suffers from the drawback that it is possible to read and copy the transmitted command signals. Afterwards, it will be possible for an unauthorized person to transmit command signals with the correct code to one or more remote-controlled units, whereby such an unauthorized person will, e.g., gain access to a building through doors, gates or windows controlled by such a remote control.
A system of this kind is known from, e.g., German publication No, DE 197 33 405 A. 30 By this remote control system, it is also possible to enter a new code on the remote control, which is in the shape of a hand-held transmitter, and transfer the new code to the remote-controlled unit in such a manner that the remote-controlled unit will subsequently react when a command signal with this new code is transmitted. However, this known system still suffers from the above-mentioned drawback unless the chosen code is changed quite often, and in theory, each time a command signal is transmitted which is highly unlikely in practice.
Also, it is known to attach particular addresses to the remote-controlled units in question in cases where a remote control must be used to control more units independently of each other, and these addresses will subsequently form part of the transmitted command signals and result in selective control of the remote-controlled units.
Such a system is known from, e.g., WO 95/02231 A concerning a remote control for a lighting arrangement. By this system, it will also be possible to read and copy the transmitted control signals, after which unauthorized control signals may be transmitted.
A further related prior art system is described in EP 0 870 889 A2. This document relates to a keyless motor vehicle entry and ignition system, in which a number of remote controls may be used for selecting a function for the vehicle to perform, e.g., unlocking the doors, via coded signals. The vehicle comprises a microcomputer for controlling these functions, and this microcomputer contains a stored list of unique identification numbers for the remote controls, by which the vehicle may be controlled. Further, a unique seed number is allocated to the microprocessor, e.g., the vehicle, and this seed number must also be stored in a storage member of each remote control for controlling the vehicle. However, this prior art system is not suitable for a device comprising a plurality of remote-controlled units since, according to this prior art, a remote controlled unit must have knowledge of identification numbers or the like for the remote controls which may be used for controlling the units. Similarly, the addition or replacement of a remote control in such a prior art system will require a lot of effort since identification number(s) or the like will have to be amended, erased and/or added in all remote-controlled units controlled by the particular remote control(s).